Supplemental environmental assessment for State Operating Permit 00095 and Federal Plan of Operations MTM-77779 : Landusky Mine operating and reclamation plan modification, acid rock drainage control and remediation

108 Pages·1993·2.7 MB·English

by  Montana. Hard Rock Bureau

MONTANA
STATE
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DOCUMENT SUMMARY
Water resources monitoring reports from the Landusky Mine show the development of acid
rock drainage (ARD) from several of the mine facilities (waste rock dumps and ore heap retaining
dikes). The current operating and reclamation plans are not designed to address ARD concerns in
detail. Modifications to these plans have been proposed by the mine operator, Zortman Mining,
Inc. (ZMI) to corredt the ARD problems. ZMI proposes to change reclamation practices for the Mill
Gulch waste rock dump, teh Sullivan Park leach pad dike and the Gold Bug pit. ZMI also proposes
to identify and selectively handle material with a high ARD generation potential as well as to con-
duct long-term reclamation studies.
ZMI's proposed modifications have been reviewed by the permitting agencies, the Montana
Department of State Lands (DSL) and the Bureau of Land Management (BLM). The agencies have
developed an alternate modification plan which expands the ZMI proposal to address all mine facili-
ties that could potentially generate ARD. This alternative would increase the reclamation capping
thickness on all heaps and waste rock dumps, reduce the slopes to ensure stability, and move the
approved Montana Gulch leach pad expansion to an existing disturbed area. This is the agencies'
preferred alternative. Other alternatives considered include the no action alternative and suspen-
sion of mine operations.
The Landusky Mine is located in the Little Rocky Mountains, Phillips County, Montana. The
mine consists of seven leach pads, four waste rock dumps, three open pit mining areas, a process-
ing plant and associated infrastructure. The mine is permitted to disturb a total of 814 acres for
mining and mining related activities.
The major rock types associated with the mine have varying degrees of acid generating and
acid neutralizing ability depending on their origin and subsequent weathering patterns. Rock types
which contain sulfide mineralization, mainly pyrite (FeSj), oxidize over geologic time and are cate-
gorized as "oxide". Rock which has not oxidized is termed "unoxidized" or sometimes "sulfide."
Other rock types in the deposit such as limestones, dolomites and shales have a natural ability to
neutralize acid.
Acid rock drainage can occur when either unoxidized or partially oxidized material that
contains sulfides comes in contact with oxygen and water. The reaction between oxygen, water
and the sulfide mineral forms acid. This reaction is accelerated by the presence of a naturally occur-
ring bacteria. The overall process is similar to natural weathering but occurs at a much faster rate
due to the increased surface area in the rock created by mining activity. Once generated, the
acidic water may come in contact with adjacent minerals that have the ability to neutralize acid. If
this neutralizing ability is exceeded the resulting discharge would be acidic. ARD may contain
levels of dissolved metals or other constituents that degrade water quality and are harmful to
aquatic life.
November 17, 1993 i
Efforts to prevent ARD are aimed at preventing water and oxygen from coming in contact
with potentially acid forming materials. This involves: identification of acid forming materials,
selective handling of those materials to place them away from possible contact with either infiltrat-
ing surface waters or groundwaters, capping of rock piles with low permeability liners to prevent
precipitation from infiltrating and limit air circulations, and diverison of runoff away from the rock
disposal area.
The efforts proposed by ZMI are consistent with this approach but may not be extensive
enough to ensure existing conditions are abated and future ARD development prevented. As a
result there is still the potential for negative impacts to both water resources and relcamation
revegetation under this alternative.
The regulatory agencies' approach is to assume that all the facilities have the potential to
produce some acid until proven otherwise. As a result the reclamation cap has been enhanced to
prevent infiltration of precipitation on not only the Mill Gulch and Gold Bug waste rock dumps, but
on all the unreclaimed leach pads and mine pits. The result is that subsequent discharge from these
facilities would be of acceptable water quality and have only a negligible impact on water resourc-
es. Surface reclamation success is likely with the lower slopes and cap of neutral material for a
capillary break. This alternative also includes increased monitoring and trend analysis to detect any
change in water quality that would require further remediation efforts.
Impacts from the no action alternative would result from continued mining under the ap-
proved operating and reclamation plans. These plans have already been demonstrated inadequate
and intermim corrective measures have been taken. To date, impacts have not been severe; how-
ever, continued operations under existing permits would most likely result in increased degradation
to water resources and partial failure of surface reclamation. Impacts from suspending current
mining permits would be very similar to those that would occur under the no action alternative.
There would be less overall mining but there would be inadequate material for reclamation. Contin-
ued mining is necessary to achieve an adequate source of neutral cap rock. This alternative was
dropped from consideration.
Implementation of corrective measures at the Landusky Mine does not require nor depend
on approval of the proposed Zortman Mine expansion.
It is the agencies' belief that implementation of the agency modified alternative would
provide the most effective means for correcting existing ARD problems and for insuring longterm
relamation success at the Landusky Mine.
Technical staff from the Montana Department of HEalth and Environmental Science, Water
Quality Bureau and the U.S. Environmental Protection Agency have provided input in the prepara-
tion of this environmental analysis. BLM and DSL appreciate their comments.
November 17, 1993 i!
....
TABLE OF CONTENTS
CHAPTER INTRODUCTION
I - 1
A. PURPOSE AND NEED FOR ACTION
1
BACKGROUND AND PROJECT LOCATION
B. 1
C. SCOPE OF ANALYSIS 5
D. AGENCY RESPONSIBILITIES 5
1. Montana Department of State Lands (MDSL) 5
2. United States Departnnent of the
Interior Bureau of Land Management (BLM) 6
3. Montana Department of Health and Environmental Sciences (DHES) ... 6
4. United States Environmental Protection Agency (EPA) 7
E. THE PERMITTING PROCESS 8
CHAPTER II - PROPOSED MODIFICATION PLAN AND ALTERNATIVES 9
A. ZMI PROPOSED MODIFICATIONS 9
B. AGENCY MODIFIED ALTERNATIVE 22
C. NO ACTION ALTERNATIVE 27
D. ALTERNATIVE EVALUATED BUT DROPPED FROM CONSIDERATION 27
CHAPTER III - AFFECTED ENVIRONMENT 31
A. GEOLOGY AND GEOCHEMISTRY 31
1 Existing Facilities 31
2. Regional Geology 34
3. Regional Geochemistry 37
B. HYDROLOGY 39
Surface Water 39
1
2. Groundwater 47
C. SOILS AND VEGETATION 50
D. WILDLIFE AND FISHERIES 51
CHAPTER IV - ENVIRONMENTAL CONSEOUENCES 53
A. GEOLOGY AND GEOCHEMISTRY 53
1 ZMI Proposed Modifications 53
2. Agency Modified Alternative 54
3. No Action Alternative 54
B. HYDROLOGY 54
1 ZMI Proposed Modifications 54
a. Surface Water 54
b. Groundwater 56
2. Agency Modified Alternative 57
November 17, 1993
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a. Surface Water 57
b. Groundwater 59
3. No Action Alternative 60
a. Surface Water 60
b. Groundwater 62
C. SOILS AND VEGETATION 63
1. ZMI Proposed Modifications 63
2. Agency Modified Alternative 64
3. No Action Alternative 65
D. WILDLIFE AND FISHERIES 65
1 ., 2. ZMI and Agency Modifications 65
3. No Action Alternative 66
CHAPTER V REASONABLY FORESEEABLE ACTIVITIES AND CUMULATIVE IMPACTS 67
-
A. REASONABLY FORESEEABLE ACTIVITIES 67
1 Exploration 67
2. Mining 67
B. CUMULATIVE EFFECTS 68
Geology and Geochemistry 68
1
2. Hydrology 69
3. Soils and Vegetation 69
4. Wildlife and Fisheries 70
CHAPTER VI - CONCLUSIONS AND RECOMMENDATIONS 71
CHAPTER CONSULTATION AND COORDINATION 73
VII -
A. PUBLIC INVOLVEMENT 73
B. INDIVIDUALS INVOLVED IN PREPARATION 74
CHAPTER GLOSSARY 75
VIII -
CHAPTER IX - REFERENCES 81
A. DOCUMENTS 81
LETTERS 83
B.
PERSONAL COMMUNICATION 85
C.
APPENDIX 86
1
November 17, 1993 JV
LIST OF FIGURES
Figure 1 : General Project Location Map 2
Figure 2: Landusky Mine Area 4
Figure 3: Mill Gulch Reclamation and Drainage 13
Figure 4: Gold Bug Waste Dump, Plan View Of 4900' Elevation 14
Figure 5: Gold Bug Waste Dump Schematic Cross Section 15
Figure 6: Cross Section Of Bench Drain Ditches 17
Figure 7: Cross Section Of Side Drain Ditches 18
Figure 8: Sullivan Park Dike Resloped Configuration 19
Figure 9: Capping Sequence 24
Figure 10: 1993 Facilities and Water Resource Monitoring Map 28
Figure 1 1 : Gold Bug Waste Repository Plan View 35
Figure 12: Geologic Map of the Little Rocky Mountains 36
Figure 13: Surface Drainage in the Landusky Area 40
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November 17, 1993
LIST OF TABLES
Table Summarv of Approved and Proposed Reclamation Plans for the Existing Landusky
1 :
^
Facilities by Drainage ^
Table 2: Characterization Of Waste Based On Total Sulfur And NNP Analyses Of 741 Sam-
20
ples
Table 3: Mine Products Characterization Program 21
Table 5: Parameter List for Water Resources Monitoring, ZMI 43
Table 6: Mill Gulch Water Quality (Sites L-25, L-26, and L-7) 46
Table 7: Water Quality at Sites L-28, L-27, and L-23 47
November 17, 1993 VI